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Power Supply Problems
WARNING
SHOCK HAZARD. Only service-trained personnel who are aware
of the hazards involved should remove the instrument covers.
The procedures in this section require that you connect the power
cord to the instrument with the covers removed. To avoid
electrical shock and personal injury, be careful not to touch the
power-line connections.
Check that the input to the supply voltage regulator is at least
1 volt greater than its output.
Circuit failures can cause heavy supply loads which may pull
down the regulator output voltage.
Check the main supply voltages as tabulated below.
Power Supply Minimum Maximum
+5 Ground Ref. 4.75V 5.25V
+5 Floating 4.75V 5.25V
-5.2 Floating -5.46V -4.94V
+18 Floating 17.0V 19.1V
-18 Floating -19.1V -17.0V
+5REF Floating 4.75V 5.25V
Some circuits produce their own local power supplies derived from
the main supplies. Be sure to check that these local supplies are
active. In particular, the output amplifier and front panel sections
have local supplies. Always check that the power supplies are free
of ac oscillations using an oscilloscope.
6
Chapter 6 Service
Troubleshooting Hints
109